Sailplane

ABSTRACT

A sailplane wherein a flexible sail is loosely connected at its corners to the ends of a rigid framework comprising a central longitudinal rod and a pair of oblique rods directed laterally and backwards, whereby during flight the sail assumes, under the air pressure, a conformation including forward portions of general positive incidence and rearward portions of general negative incidence.

I United States Patent 1191 1111 3,801,052 Quercetti Apr. 2, 1974SAILPLANE 2,463,135 3 1949 Bach 244/153 R 3,347,500 10/1967 Hartig....244/153 R [76] Alessandro Q 3,276,730 10 1966 Cleveland 244 153 RBaffloneccha 77/16, 3,305,198 2/1967 Sellers, Jr 244 153 R Tormo, Italy3,018,075 1/1962 Bowers...'. 244 153 R [22] Filed: Oct. 30, 1972 PrimaryExaminer+Trygve M. BllX PP 30 ,805 Assistant Examiner-Paul E. SaubererAttorney, Agent, or Firm-Young and Thompson [30] Foreign ApplicationPriority Data Nov. 16, 1971 Italy 70739 71 [57] ABSTRACT A sailplanewherein a flexible sail is loosely connected [52] U.S. Cl 244/153 R atits corners to the ends of a rigid framework com- [51] Int. Cl. B64c31/06 prising a central longitudinal rod and a pair of oblique [58]Field of Search 244/153 R, 154, 155 R, rods directed laterally andbackwards, whereby during 244/DIG. l flight the sail assumes, under theair pressure, a conformation including forward portions of general posi-[56] References Cited tive incidence and rearward portions of generalnega- UNITED STATES PATENTS mcldence- I 2,537,560 1 1951' Wanner 244 153R 9. Claims, 7 Drawin Figures PATENTED R 2 i974 F'|G.S Has FIG.4

SAILPLANE BACKGROUND OF THE INVENTION This invention relates to asailplane whose construction is unexpensive and whose performance isgood.

As is known, the sailplanes having stability features and especiallyaerodynamic efficiency features, such as to assure a long lastingflight, an efficacious height elevation by traction effect and a goodutilization of the ascending currents encountered, do not lendthemselves to economical industrial manufacture.

BRIEF SUMMARY OF THE INVENTION The first object of the invention is toprovide a sailplane suitable to be used either as a toy or for sportingobjects, for meteorologic observations and for the transport ofsuspended objects, which due to a particular configuration of its activeaerodynamic surfaces presents marked features of longitudinal,transverse and heading stability, together with a remarkably highaerodynamic efficiency, so that its performances are clearly moresatisfactory than those of the known analogous sailplanes.

Another object of the invention is to provide a sailplane suitable toplane with a good efficiency while still engaged to the tow cable, sothat it may switch from the free flight to the towed flight and viceversa, simply by actuating or interrupting the towing action, to permita control from ground at least concerning the distance from the operatorand some simple manipulations, these features being particularlyintended to permit the use of the sailplane within a limited space aswell as to facilitate its use which, in the versions having a toycharacter, is also suitable for school-children.

Said objects are attained, according to the invention, by means of asailplane of the type comprising a framework and a sail formed by asheet of a flexible material connected at its vertices to saidframework, characterized in that said framework comprises a central rodlocated along a longitudinal central line of the sailplane, a rigidconnecting element along said central rod in its front half, and a pairof oblique rods rigidly connected to said connecting element andextending towards the backward section of the sailplane forming an acuteangle with respect to said central rod, and in that the sheet offlexible material forming the sail is connected to the ends of said rodsforming the framework and its dimensions exceed the framework dimensionsso that it is loose or flabby at rest and assumes when flying, due tothe effect of the air pressure, a configuration including two forwardportions located in front of the oblique rods and having a generalpositive incidence, and two rear portions located behind the obliquerods, having a general negative incidence and forming a pair of channelswhich diverge with respect to the longitudinal central line of thesailplane.

It has been ascertained that the mutual cooperation of these forward andrear portions of the sail produces aerodynamic effects partiuclarlyfavourable, if considering separately the qualities of said singleportions of the sail. In this effect both the forward and the rearportions contribute to the lift, the forward portions contributeprincipally to the longitudinal stability, and the rear portions, due totheir divergent channel shape, contribute principally to the transversestability, which is particularly high, so that there is no need to giveto This feature provides advantageous conditions for the behaviour ofthe sailplane, particularly because the stress applied to the rearportions of the sail is transmitted through the orientable ends to theforward portions of the sail, deforming them and displacing in anadvantageous manner the pressure center.

Preferably, the plan view shape of the sail substantially derives from asquare or a rhombus located with a diagonal along said longitudinalcenter line, the rear vertex of said square or rhombus being cut offalong a line nearly perpendicular to said longitudinal center line, andsaid oblique lines terminate at the side vertices of said square orrhombus.

The distance between the side .vertices of said square or rhombus beingdefined as the wing span, the length of the sail between its forward endand its after end is preferably comprised between 65% and 90% preferablythe 82% of the wing span, and the distance of forward end of the sailfrom the point of the longitudinal center line where said oblique rodsdepart is preferably comprised between 10% and 25% (preferably 15%) ofthe wing span, while the length of the rear transverse side of the sailis preferably comprised between 25% and 50% (preferably 38%) of the wingspan. The angle formed between each of said oblique rods and the rearpart of the longitudinal center line is preferably comprised between 40and (preferably 55) BRIEF DESCRIPTION OF THE DRAWINGS The particularfeatures and the operation of the sailplane according to the inventionwill more clearly appear from the following specification of anexemplifying and not limiting embodiment, schematically represented onthe accompanying drawing, wherein:

FIG. 1 is a plan view, on a very reduced scaple, of a sailplaneaccording to the invention;

FIG. 2 is a cross section along line B-E of FIG. I, viewed in thedirection of arrow II;

FIG. 3 is a cross section along line IIIIIIIII of FIG. 1 and viewed fromthe rear; FIGS. 2 and 3 showing the sailplane in flight conditions;

FIG. 4 illustrates on cross section and in a larger scale the detail ofan orientable member connecting the wing ends;

FIG. 5 illustrates a longitudinal cross section of a member for thecoupling of the tow cable;

FIG. 6 is a view of the front part of the coupling DETAILED DESCRIPTIONOF THE PREFERRED EMBODIMENT Geometrically, the sail of the sailplane issymmetrical with respect to a longitudinal center line a and isdelimited by two front sides b, b which extend between the forward end Aand the side vertices B,B, by two inclined rear sides c,c extendingbetween the lateral vertices 13,8 and rear vertices C,C, and by a reartransverse side d extending between the rear 'vertices C,C and passingthrough the after end D of the sail. Each of the right hand and the lefthand parts ABCD of the sail, which are symmetrical with respect to linea, is subdivided in two portions: 1 the forward and 2 the rear, by anoblique line e extending from a point E, located in the forward half ofline a, to the lateral vertex B. The

lateral vertices B lie in a same plane with the central line a.

The sail is formed by a sheet of a substantially flexible material whichmay preferably be a thin rolled polyester, and cooperates with asubstantially rigid framework formed, e.g., by rods of wood or othersuitable and relatively light material. in said framework, alongitudinal rod 3 materializes the longitudinal center line a, twooblique bars 4 materialize the oblique lines e and a junction member 5materializes point E, and four connecting members 6, 7, 8, locatedbetween-the sail and the ends of rods 3 and 4,-materialize the forwardand after points A and D as well as the lateral vertices or wing endsB,B. But the dimensions of the sail are slightly greater with respect tothe lengths of the rods, so that in the rest condition (F IG. 5) thesail is applied loosely to the underside of the framework.

In flight, the whole lift and resistance effects applied to the sailinclude pressures which are perpendicular to the same sail and put it intension with respect to the framework but, due to the greater dimensionsof the sail, this assumes an arcuate configuration, with respect to theframework, with the concavity facing downward and, precisely, theforward portions I assume a positive incidence and the rear portions 2assume a negative incidence and divergent channel shapes with respect tothe central rod 3. 1

The sail forward portions 1 having a positive icidence, besides theircontribution to the lift, givean essential contribution to thelongitudinal stability of the Sailplane.

Therear portions 2 of the sail, shaped as described, generate, forreasons which are not yet completely clear, an aerodynamic effect highlystabilizing on the transverse trim of the Sailplane, while the greaterencumbrance of the rear curved surfaces, viewed from the sides, withrespect to the forward surfaces, causes a backward displacement of thelateral pressure center with respect to the barycenter, whoseconsequence is a high heading stability.

The aerodynamic efficiency of the sail assembly so formed is remarkablyhigh and, ensures the capability of the sailplane to plane with a stabletrim and heading, with a slight gliding angle,in calm air, to riserapidly by traction effect obtained by means of a cable 9 dragged withrespect to the calm air or retained withrespect to the wind, and to keepat height under the effect of even the slightest ascensional currentsencountered.

It has been ascertained that while keeping steady the specifiedarrangement, the efficiency and the stability of the sailplane may beincreased by providing some orientability, relative to the framework,for the wing ends of the sail, so that under the stresses applied bytheair during flight, the ends of the sail forward portions displaceslightly downward. This displacement is due to the prevalent forcesacting on the sail rear portions giving them a negative incidence, andto the fact that this negative incidence is transmitted to the sailforward portions as the effect of the orientability of the wing ends.This causes a displacement of the pressure centers on the sail forwardportions and it is thought this is the principal reason of theascertained increase of stability and aerodynamic efficiency.

The desired orientability of the wing ends, has been obtained with verysimple and economical means by providing each of the caps 8, intended tobe inserted on the outer ends of the lateral rods 4 of the framework,with an extension blade 8' formed integrally with the cap 8 by moldingfrom a suitable synthetic material. Blade 8', which is provided with anadhesive layer on its lower face, is an excellent means for thefastening of the connecting members 8-8 onto the wing ends, that is, incorrespondence with the lateral vertices of the synthetic material sheetforming the sail. Cap 8 is rotatingly inserted, that is' not forced,onto the end of the corresponding lateral rod 4. The wing ends sosustained with mobility orientate, in flight, as indicated in FIGS. 2and 3, namely the sail rear portion 2, assuming a negative incidence,drags with it blade 8' rotating cap 8 on rod 4 and thereby transmits acorresponding nega' tive incidence to the side end of the sail forwardportion 1, as particularly illustrated in greater scale on FIG. 7, ascompared with the plane configuration at rest indicated by a chain lineon the same figure.

This arrangementassures further the advantage of a reduction of thelength of the Sailplane lateral rods 4, for the same wing span, with aconsequent reduction of the weight and cost and displacement of thebarycenter. It has been ascertained that the described arrangementimproves further the behaviour of the sailplane during towing in thepresence of a lateral wind.

A connecting member 7-7 substantially similar to member 8-8 described,may be opportunely used for the connection of the longitudinal rod 3 tothe tail D of the sail, contributing thereby to the forward displacementof the barycenter. ln this case, some elastic flexibility of blade 7becomes important, as has been ascertained, because it favorsparticularly the Sailplane stability during towing.

Also, an analogous connecting member 6-6, having the blade 6' on theopen side of cap 6 instead of the closed side, may be used to connectthe sail forward end A to the central rod 3'.

The general shape of the sail preferably derives from a square ABFBAlocated with a diagonal AF along the longitudinal central line a, andfrom which a triangular rear part CFC has been cut off with a transversecut d passing through the after point D.

As the rear edges of the sail are likely to flap under certainconditions, and this may be undesirable, they may be stiffened, ifdesired, with rods 13 connected to the rear portions of sail 2, saidrods starting from vertices C of the sail and being directed towards thejunction member 5 (point E) but without reaching it.

In consideration of the well known opportunity to form with wood theframework of sailplanes and kites and the impossibility ofstandardization of said mate:

rial, it should be necessary for the construction to select pairs ofidentical rods to form the lateral parts 4 of the framework in order tohave the barycenter and the rect alignment of the traction center, thegravity center and the pressure center in order to have correct towing.This involves an operation for the selection and assortment of the rodswhich is industrially inconvenient.

in order to permit compensation of any accidental lateral displacementof the barycenter and the pressure center, instead of systematicallyavoiding said displacement, the sailplane has been provided with amember for the coupling of the traction cable 9, substantially asrepresented in FIGS. 5 and 6. It comprises a sleeve shaped part to befirmly connected to the rods located along the median axis a of theframework, and a lower flange 11 which is provided with a plurality ofconnection pins 12 arranged side by side of one another so that one ofthem lies on the center line while the others are more or less laterallydisplaced, to the right hand and left hand respectively. By a suitableselection of the pin 12 to which the traction cable 9 is coupled ortied, it is possible to locate the traction center in a convenientposition with respect to the barycenter and the pressure center, even ifthese are accidentally slightly displaced with respect to the centerline a.

This arrangement permits also improving the behaviour of the sailplane,by the introduction of a wilful] lack of alignment between said centers,in case the sailplane is to be towed, for its lift, along a directionwhich is transverse to the direction of the wind, namely in conditionsof lateral wind.

As the coupling member 10 must not be allowed to rotate around thecenter line a, said member is suitably connected to the junction member5 by means ofa rod 3 which is not round, which may be advantageouslyformed by a structural shape, for example H shaped, of a rigid syntheticmaterial. In this way the longitudinal rod of the framework is formed bythree sections, forward 3', median 3" and rear 3, whose extreme sections3 and 3 are advantageously wood rods having a circular cross section,While the intermediate section is a non circular structural shape of asynthetic material.

In the arrangement now preferred, the length of the wing span beingindicated by BB, the length from prow to stern AD is about 82% of thewing span, the distance AE between the prow and the point from which theoblique lines e start, is 15% of the wing span, and the length of therear side a' is about 38% of the wing span. The angle BED formed by theoblique lines 2 with respect to the rear portion of the longitudinalcenter line a is about 55.

Nevertheless it must be noted that said proportion may be modified invarious ways. It is thought that the distance prow-stern may bepreferably comprised between 65% and 90% of the wing span, the distancebetween the prow and the point from which the oblique lines 2 start maybe preferably comprised between 10% and 25% of the wing span, and thelength of the rear transverse side may be preferably comprised between25% and 50% of the wing span, while the angle BED may be generally andpreferably comprised between 40 and 75+. Further, the angles ABC and BABare not necessarily right angles but they may be generally comprisedbetween 60 and 120, that is, the ideal square ABFB may be replaced by awidened or lengthened rhombus, or generally by a quadrilateral.

It is further to be kept in mind that the rectilinear segments b, c, d,2 represent the scheme of the sailplane construction, but that inpractice they may be replaced by curves or by sinuous or broken lineseither for technical or for aesthetical reasons. Therefore, as anexample, the forward sides b may present a slightly concave line whilethe sides c, d may be replaced by a single curve, and lines e maypresent central sections perpendicular or nearly perpendicular to thecentral line a. Further, in correspondence of the prow and stem pointsA, D, the sail may have extensions which are of no efficacy foraerodynamic purposes but serve e.g. to simulate the shape of a cockpit.

Rods 3, 4 may be connected one to another by a junction member 5 whichpresents short tubular branches intended to receive the ends of therods, in a manner well known eg in the construction of kites. As alreadysaid, the sailplane does not require a lateral V shape, and hence saidjunction member may be planar. It must yet be understood that notechnical reason prevents one from giving to the sailplane a Vconfiguration if considered preferable, as for example for aestheticalreasons.

Having thus described my invention, what I claim is:

1. In a sailplane comprising a substantially rigid framework and aflexible sail,

said framework comprising a central rod extending in the longitudinaldirection of the sailplane, along said central rod in the forwardportion thereof, a

rigid connection member, and a pair of oblique rods fixedly connected tosaid connection member and extending towards the rear portion of thesailplane forming an acute angle with respect to said centrallongitudinal rod,

said sail comprising a sheet of a flexible material having cornersconnected to the ends of said rods of the framework;

the improvement in which said sheet has from edges which aresubstantially longer than the distances between the forward end of saidcentral rod and the free ends of said oblique rods, and has rear edgeswhich are substantially longer than the distances between the rear endof said central rod and the free ends of said oblique rods whereby saidsail is loose on said framework at rest and assumes during flight, dueto the effect of air pressure, a configuration including two forwardportions located in front of said oblique rods and on the right and theleft respectively of the forward portion of said central rod, saidforward portions of the sail having a positive aerodynamical incidence,and two rear portions located behind said oblique rods and on the rightand the left respectively of the rear portion of said central rod, saidrear portions of the sail having a negative aerodynamical incidence, andforming a pair of channels which diverge with respect to said centrallongitudinal rod of the framework of the sailplane.

2. In a sailplane as set forth in claim 1, a pair of connecting caps,each connecting cap having a sleeve portion and an extension integralwith said sleeve portion,

the extensions of said connecting caps being joined to theflexible sheetforming the sail in vicinity of the corners thereof which are moreremote from said central rod of the framework, and the sleeve portionsof said connecting caps being inserted rotatably upon the ends of saidoblique rods, opposite said connection member.

3. In a sailplane as set forth in claim 1, a rear connecting cap havinga sleeve portion and an extension integral with said sleeve portion,said extension being resiliently flexible and being joined to theflexible sheet forming the sail at the rear end thereof, and the sleeveportion of said rear connecting cap being inserted upon the rear end ofsaid central rod of the framework.

4. A sailplane as set forth in claim 1, wherein said flexible sheetforming the sail has a shape derived from a'quadrilateral with at leastapproximately equal sides, located with two opposite corners alignedwith said central rod of the framework, and a triangular rear portion ofwhich is cut off along a line transverse to said central rod.

5. A sailplane as set forth in claim 1, further comprising a couplingmember fixedly connected to said central rod of the framework, saidcoupling member having a number of coupling pins located side by side onsaid coupling member along a direction transverse to said central rod,said coupling pins selectively receiving the coupling of a tractioncable for the Sailplane.

6. A Sailplane as set forth in claim 1, further comprising a couplingmember fixedly connected to said central rod of the framework behindsaid rigid connection member, said coupling member having a number ofcoupling pins located side by side on said coupling member along adirection transverse to said central rod, and said central rodcomprising three separate portions, namely a front portion located infront of said connection member, an intermediate portion located betweensaid connection member and coupling member, and a rear portion locatedbehind said coupling member, said intermediate portion of the centralrod being formed by a short non circular structural shape of a syntheticmaterial and being connected nonrotatably to said connection member andcoupling member.

7. A Sailplane as set forth in claim 1, further comprising a pair ofstiffening rods, each stiffening rod being fixedly joined to theflexible sheet forming the sail, and extending from a rear and lateralpoint of said sheet towards a point of the forward portion of saidcentral rod of the framework, without however attaining said centralrod.

8. A Sailplane as set forth in claim 1, wherein the length of theflexible sheet forming the sail is comprised between 65% and 90% of themaximum width of said sheet, the distance from the forward end of saidcentral rod of the framework and said connection member is comprisedbetween 10% and 25% of said maximummentioned length is about 38%.

* =k =l= =l=

1. In a sailplane comprising a substantially rigid framework and aflexible sail, said framework comprising a central rod extending in thelongitudinal direction of the sailplane, along said central rod in theforward portion thereof, a rigid connection member, and a pair ofoblique rods fixedly connected to said connection member and extendingtowarDs the rear portion of the sailplane forming an acute angle withrespect to said central longitudinal rod, said sail comprising a sheetof a flexible material having corners connected to the ends of said rodsof the framework; the improvement in which said sheet has front edgeswhich are substantially longer than the distances between the forwardend of said central rod and the free ends of said oblique rods, and hasrear edges which are substantially longer than the distances between therear end of said central rod and the free ends of said oblique rodswhereby said sail is loose on said framework at rest and assumes duringflight, due to the effect of air pressure, a configuration including twoforward portions located in front of said oblique rods and on the rightand the left respectively of the forward portion of said central rod,said forward portions of the sail having a positive aerodynamicalincidence, and two rear portions located behind said oblique rods and onthe right and the left respectively of the rear portion of said centralrod, said rear portions of the sail having a negative aerodynamicalincidence, and forming a pair of channels which diverge with respect tosaid central longitudinal rod of the framework of the sailplane.
 2. In asailplane as set forth in claim 1, a pair of connecting caps, eachconnecting cap having a sleeve portion and an extension integral withsaid sleeve portion, the extensions of said connecting caps being joinedto the flexible sheet forming the sail in vicinity of the cornersthereof which are more remote from said central rod of the framework,and the sleeve portions of said connecting caps being inserted rotatablyupon the ends of said oblique rods, opposite said connection member. 3.In a sailplane as set forth in claim 1, a rear connecting cap having asleeve portion and an extension integral with said sleeve portion, saidextension being resiliently flexible and being joined to the flexiblesheet forming the sail at the rear end thereof, and the sleeve portionof said rear connecting cap being inserted upon the rear end of saidcentral rod of the framework.
 4. A sailplane as set forth in claim 1,wherein said flexible sheet forming the sail has a shape derived from aquadrilateral with at least approximately equal sides, located with twoopposite corners aligned with said central rod of the framework, and atriangular rear portion of which is cut off along a line transverse tosaid central rod.
 5. A sailplane as set forth in claim 1, furthercomprising a coupling member fixedly connected to said central rod ofthe framework, said coupling member having a number of coupling pinslocated side by side on said coupling member along a directiontransverse to said central rod, said coupling pins selectively receivingthe coupling of a traction cable for the sailplane.
 6. A sailplane asset forth in claim 1, further comprising a coupling member fixedlyconnected to said central rod of the framework behind said rigidconnection member, said coupling member having a number of coupling pinslocated side by side on said coupling member along a directiontransverse to said central rod, and said central rod comprising threeseparate portions, namely a front portion located in front of saidconnection member, an intermediate portion located between saidconnection member and coupling member, and a rear portion located behindsaid coupling member, said intermediate portion of the central rod beingformed by a short non circular structural shape of a synthetic materialand being connected non-rotatably to said connection member and couplingmember.
 7. A sailplane as set forth in claim 1, further comprising apair of stiffening rods, each stiffening rod being fixedly joined to theflexible sheet forming the sail, and extending from a rear and lateralpoint of said sheet towards a point of the forward portion of saidcentral rod of the framework, without however attaining said centralrod.
 8. A sailplane As set forth in claim 1, wherein the length of theflexible sheet forming the sail is comprised between 65% and 90% of themaximum width of said sheet, the distance from the forward end of saidcentral rod of the framework and said connection member is comprisedbetween 10% and 25% of said maximum width, the angle formed by saidoblique rods with respect to said central rod is comprised between 40*and 75* and the flexible sheet forming the sail has a rear transverseside whose length is comprised between 25% and 50% of said maximumwidth.
 9. A sailplane as set forth in claim 8, wherein saidfirst-mentioned length is about 82%, said distance is about 15%, saidangle is about 55*, and the second-mentioned length is about 38%.